Option D is correct because the suffix -ish is used in the formation of adjectives indicating the quality or characteristic of that noun. For example, in the sentence "Stacy was foolish to believe him", the adjective 'foolish' modifies the noun 'Stacy'. Option C is incorrect because 'fooled' is a verb, meaning 'being deceived'. 'Foolful' and 'foolly' are not words, they do not exist in the English dictionary, hence options A and B are incorrect.